Brad L. Kinsey

An Analytical Model for Tailor Welded Blank Forming

Tailor Welded Blanks (TWBs) offer several notable benefits including decreased part weight, reduced manufacturing costs, increased environmental friendliness, and improved dimensional consistency. In order to take advantage of these benefits, however, designers need to overcome the reduced formability of TWBs and be able to accurately predict unique characteristics related to TWB forming early in the design process. In this poper, an analytical model to predict the weld line movement and forming height for a uniform binder force, TWB forming application is presented. Comparison to numerical simulation results demonstrates the accuracy of this methodology. The analytical model provides designers a valuable tool to determine the location of steps on the die surface to accommodate the weld line movement and the potential forming height for a TWB forming with a uniform binder force. The methodology presented here has the potential to be extended to analyze a non-uniform binder force forming of TWBs.

Investigation of deformation size effects during microextrusion

Microextrusion has recently emerged as a feasible manufacturing process to fabricate metallic micropins having characteristic dimensions on the order of less < 1 mm. At this length scale, the deformation of the workpiece is dominated by the so-called size effects, e.g., material property and frictional behavior variations at small length scales. In extrusion experiments performed to produce submillimeter-sized pins having a base diameter of 0.76 mm and an extruded diameter of 0.57 mm, the extruded pins exhibited a curving tendency when a workpiece with a relatively coarse grain size of 211 μm was used. This phenomenon was not observed when workpieces with a finer grain size of 32 μm were used. In this paper, results from microhardness tests and microstructure analyses for both grain sizes are presented to investigate this phenomenon and to characterize the deformation during microextrusion. The results obtained from this analysis show that as the grain size approaches the specimen feature size, the deformation characteristics of the extruded pins are dominated by the size and location of specific grains, leading to a nonuniform distribution of plastic strain and measured hardness and, thus, the curving tendency. Microhardness tests of the initial billet material and tensile test specimens are also presented as supplementary analyses.

Experimental Implementation of Neural Network Springback Control for Sheet Metal Forming

The forming of sheet metal into a desired and functional shape is a process, which requires an understanding of materials, mechanics, and manufacturing principles. Furthermore, producing consistent sheet metal components is challenging due to the nonlinear interactions of various material and process parameters. One of the major causes for the fabrication of inconsistent sheet metal parts is springback, the elastic strain recovery in the material after the tooling is removed. In this paper springback of a steel channel forming process is controlled using an artificial neural network and a stepped binder force trajectory. Punch trajectory, which reflects variations in material properties, thickness and friction condition, was used as the key control parameter in the neural network. Consistent springback angles were obtained in experiments using this control scheme.

Deformation Size Effects Due to Specimen and Grain Size in Microbending

Sheet metal forming often consists of bending processes in which gradients of deformation exists through the thickness of the workpiece in a localized deformation area. In microscale bending, these deformation gradients become much steeper, as the changes in the deformation occur over short distances (in the order of micrometers). In addition, with miniaturization, the number of grains that are present through the thickness decreases significantly. In this research, the effect of grain size and specimen size on the deformation distribution through the thickness of microbent sheet specimens was investigated via microhardness evaluations. It was found that the deformation distribution, i.e., hardness profile, is not affected significantly by the grain size when the sheet thickness is large (for 1.625 mm specimens) or by miniaturization of the specimen size when the grain size is fine. However, the deformation distribution of the coarse grained specimens deviates from the fine grained ones and from the 1.625 mm thick sheet specimens when thespecimen size is miniaturized.

Recent Advances in Micro/Meso-Scale Manufacturing Processes

The development of new manufacturing processes and process enhancements at the micro/meso-scale has expanded considerably in recent years due to the demand for miniaturized products. With this increased demand comes a critical need for a fundamental understanding of the role these reduced length scales play in the various process mechanisms. Significant research has been recently performed on a wide range of micro/meso-scale manufacturing processes to understand the role of the tribological effect, size effect and other mechanisms on process performance. This paper reviews the research and state-of-the-art for micro/meso-scale mechanical cutting and related machine technologies, micro-EDM, laser micro-machining and laser shock peening, microforming, and micro-scale bio-manufacturing and polymer fabrication. These latter areas may be of particular interest as they have not received as much attention as the traditional process areas.Copyright

The effect of engineering major on spatial ability improvements over the course of undergraduate studies

Spatial ability, which is positively correlated with retention and achievement in engineering, mathematics, and science disciplines, has been shown to improve over the course of a Computer-Aided Design course or through targeted training. However, whether increases in spatial ability are obtained from freshman to senior years simply by completing courses in an engineering curriculum has not been investigated. Furthermore, whether the spatial ability of undergraduate students affects their choice of engineering major has not been studied. To provide data with respect to these questions, portions of the Purdue Spatial Visualization Test (PSVT) were administered to freshman and senior students from various engineering disciplines within a College of Engineering and Physical Science (CEPS). In addition, a self efficacy test, which was developed to assess the self confidence of students related to spatial tasks, was also administered. Data analysis showed that spatial ability, while an important parameter for retention and achievement, does not affect the choice of major for engineering students. The data indicated that the spatial ability of students in engineering majors which rely more heavily on spatial ability skills (e.g. mechanical engineering) improved more than other engineering majors.

Effect of Yield Criterion on Numerical Simulation Results Using a Stress-Based Failure Criterion

Determining tearing concerns in numerical simulations of sheet metal components is difficult since the traditional failure criterion, which is strain-based, exhibits a strain path dependence. A stress-based, as opposed to a strain-based, failure criterion has been proposed and demonstrated analytically, experimentally in tube forming, and through numerical simulations. The next step in this progression to the acceptance of a stress-based forming limit diagram is to demonstrate how this failure criterion can be used to predict failure of sheet metal parts in numerical simulations. In this paper, numerical simulation results for dome height specimens are presented and compared to experimental data. This procedure was repeated for various yield criteria to examine the effect of this parameter on the ability to predict failure in the numerical simulations. Reasonable agreement was obtained comparing the failure predicted from numerical simulations and those found experimentally, in particular for the yield criterion which has been shown to best characterize the material used in this study.

Residual Ductility and Microstructural Evolution in Continuous-Bending-under-Tension of AA-6022-T4

A ubiquitous experiment to characterize the formability of sheet metal is the simple tension test. Past research has shown that if the material is repeatedly bent and unbent during this test (i.e., Continuous-Bending-under-Tension, CBT), the percent elongation at failure can significantly increase. In this paper, this phenomenon is evaluated in detail for AA-6022-T4 sheets using a custom-built CBT device. In particular, the residual ductility of specimens that are subjected to CBT processing is investigated. This is achieved by subjecting a specimen to CBT processing and then creating subsize tensile test and microstructural samples from the specimens after varying numbers of CBT cycles. Interestingly, the engineering stress initially increases after CBT processing to a certain number of cycles, but then decreases with less elongation achieved for increasing numbers of CBT cycles. Additionally, a detailed microstructure and texture characterization are performed using standard scanning electron microscopy and electron backscattered diffraction imaging. The results show that the material under CBT preserves high integrity to large plastic strains due to a uniform distribution of damage formation and evolution in the material. The ability to delay ductile fracture during the CBT process to large plastic strains, results in formation of a strong <111> fiber texture throughout the material.

Investigation of deformation characteristics of micropins fabricated using microextrusion

Microextrusion has recently emerged as a feasible manufacturing process to fabricate metallic micropins having characteristic dimensions of the order of less than 1 mm. At this length scale the deformation of the workpiece is dominated by the so-called ‘size effects’, e.g. material properties and frictional behavior vary at small length scales. In recent extrusion experiments performed to produce sub-millimeter sized pins having a base diameter of 0.76 mm and an extruded diameter of 0.57 mm, certain interesting deformation characteristics were observed. When a workpiece with a relatively large grain size of 211 μm was used, the billet tended to deform inhomogenously, and the extruded pins showed a tendency to curve. This phenomenon was not seen when workpieces with a smaller grain size of 32 μm were used. It is believed that the relative size and orientation of the large grains in the 211 μm grain size sample are responsible for this behavior and the aim of this paper is to investigate this phenomenon. Microindentation tests were performed on micropins extruded from workpieces of both grain sizes to obtain a measure of the distribution of induced strain. The results obtained from this analysis show that the deformation characteristics of the extruded pins are dominated by the size and location of specific grains leading to a non-uniform distribution of plastic strain and measured hardness.Copyright

Comparison of Analytical Model to Experimental and Numerical Simulations Results for Tailor Welded Blank Forming

Tailor welded blanks (TWBs) offer several notable benefits including decreased part weight, reduced manufacturing costs, and improved dimensional consistency. However the reduced formability and other characteristics of the forming process associated with TWBs has hindered the industrial utilization of this blank type for all possible applications. One concern with TWB forming is that weld line movement occurs, which alters the final location of the various materials in the TWB combination. In this technical brief, an analytical model to predict the initial weld line placement necessary to satisfy the desired, final weld line location and strain at the weld line is used. Results from this model are compared to an experimental, symmetric steel TWB case and a 3D numerical simulation, nonsymmetric aluminum TWB case. This analytical model is an extension of one previously presented, but eliminates a plane strain assumption that is unrealistic for most sheet metal forming applications. Good agreement between the analytical model, experimental, and numerical simulation results with respect to initial weld line location was obtained for both cases. Results for the model with a plane strain assumption are also provided, demonstrating the importance of eliminating this assumption.